1. Field of the Invention
This invention relates to drive mechanisms and more particularly to a ground wheel drive apparatus for use with farm machinery.
2. Description of the Prior Art
Mechanized farm machinery have utilized ground wheel drive devices for some time to provide auxiliary power to drive seed planters, fertilizer applicators, herbicide applicators and other similar devices. The most common of such farm machines is a tractor having an adjustable device commonly referred to as a toolbar on the back thereof. Although toolbars are used to accomplish various tasks, in this application, a plurality of seed planters, fertilizer applicators or herbicide applicators, hereinafter simply referred to as applicators, are mounted in spaced increments along the length of the toolbar, and are operated by a single drive shaft which is spaced above and parallel with respect to the toolbar. The single drive shaft is connected to each of the applicators so that rotation of the drive shaft will simultaneously operate the applicators.
In accomplishing tasks of this nature, it is important that the applicators operate at a speed which corresponds to the speed of the tractor to insure uniform material application. For this reason, the ground wheel drive device is the most desirable power source for this purpose.
Prior art ground wheel drive devices of the most commonly used type are clamped onto the toolbar and provide a rigid plate extending rearwardly therefrom. A trailing frame is pivotably mounted on the rearmost end of the rigid plate, and a ground engaging wheel is rotatably journaled at the rearmost end of the trailing frame. In this manner, the trailing frame is free to pivotably move in response to the ground wheel following the contour of the land when the device is pulled along behind the tractor, and in response to bouncing or other movements of the tractor.
The ground engaging wheel rotatably drives a transverse drive shaft, by means of a first chain-sprocket assembly, with the transverse drive shaft being rotatably journaled on the trailing frame adjacent the forward end thereof. A second chain-sprocket assembly interconnects the transverse drive shaft of the ground wheel drive device with the applicator drive shaft. A spring-loaded idler sprocket assembly is provided on the rigid plate and is biased so as to engage the non-pulling, or slack, portion of the chain of the second chain-sprocket assembly.
The above described prior art ground wheel drive device is very troublesome in that the chain of the second chain-sprocket assembly is subject to jumping off, i.e., becoming disengaged from, the sprockets upon changes of more than a minor nature in the trailing attitude of the trailing frame, and when the tractor is backed up.
When the prior art ground wheel device is being attached to the toolbar, the chain of the second chain-sprocket assembly is adjusted to have the proper tension when an aligned relationship exists between the applicator drive shaft, the pivot axis of the trailing frame and the transverse drive shaft. When any change in the trailing attitude of the trailing frame occurs as a result of the ground engaging wheel encountering an irregularity in the land, the transverse drive shaft will be moved in an arcuate path about the pivot axis of the trailing frame. Such movement of the transverse drive shaft will alter the above described aligned relationship and will shorten the distance between the applicator drive shaft and the transverse drive shaft with a resulting loosening of the chain. When the change in the attitude of the trailing frame is relatively small, the spring-loaded idler sprocket will automatically maintain proper tension on the chain. However, relatively large changes in the attitude of the trailing frame, say for example, of more than five or six inches of arcuate movement of the wheel about the pivot axis of the frame, the idler sprocket cannot take up all the resulting looseness of the chain and the loosened chain will easily become disengaged.
When the tractor is backed up, the ground engaging wheel will be rotated in a reverse direction and the heretofore slack portion of the chain will become the taut portion and the chain will reverse its direction. These actions force the idler sprocket out of engagement with the chain and the resulting looseness of the chain will cause it to jump off of its sprockets.
The physical location of the ground wheel drive apparatus is such that the operator of the tractor cannot watch it constantly. However, due to the chain jumping problem of the prior art structures, he must make periodic checks. Whenever the chain of the ground wheel drive assembly does become disengaged, it is a very time consuming and frustrating occurrence for the operator in that he must not only reinstall the chain, he must back up the tractor to rework the ground missed during the time that his equipment was inoperative.
Therefore, a need exists for a new and improved ground wheel drive apparatus which overcomes some of the problems and shortcomings of the prior art.